1. Field of the Invention
The invention relates to the use of particular phosphoric esters as emulsifiers and dispersants for pigments and fillers, based on polystyrene-block (b)-polyalkylene oxide copolymers.
2. Description of the Related Art
The invention relates to the use of particular phosphoric esters as emulsifiers and dispersants for pigments and fillers, based on polystyrene-block (b)-polyalkylene oxide copolymers.
Phosphoric esters and their use as dispersants are known and can be found in the prior art. For instance, U.S. Pat. No. 4,720,514 describes phosphoric esters of a series of alkylphenol ethoxylates which may be used advantageously to formulate aqueous pigment dispersions. Phosphoric esters for a similar application are described by EP-A-0256427. Furthermore, DE-3542441 discloses bisphosphoric monoesters of block copolymers and salts thereof. It also describes their possible use as dispersants and emulsifiers, in particular for preparing crop protection formulations. U.S. Pat. No. 4,872,916 describes the use of phosphoric esters based on alkylene oxides of straight-chain or branched aliphatics as pigment dispersants. Similarly, U.S. Pat. No. 3,874,891 describes the use of corresponding sulfates. The documents U.S. Pat. Nos. 5,130,463 and 5,151,218 report on phosphoric esters based on hydroxy-terminated polyadducts and polycondensation products, respectively, which are used to produce highly filled polyester molding compounds, in particular for SMC and BMC formulations (SMC=sheet molding compounds; BMC=bulk molding compounds). Bifunctional phosphoric esters, prepared by the Mannich-Moedritzer reaction, and their adsorption characteristics on calcium carbonate are described by J. Appl. Polym. Sci. 65, 2545 (1997). U.S. Pat. No. 4,456,486 describes, inter alia, acidic or neutral phosphoric esters of fatty alcohols and alkoxylated fatty alcohols as treatment compositions for certain blue pigments. Similarly, EP-A-256427 describes the use of phosphoric esters of alkoxylated fatty alcohols to prepare pigment dispersions said to be suitable for aqueous applications. U.S. Pat. No. 4,720,514 describes pigment dispersions prepared using phosphoric esters of alkoxylates of differing structure. U.S. Pat. No. 4,698,099 describes pigment dispersions comprising, as dispersants, phosphoric esters of monohydroxy-terminated polyesters.
DE-A-3930687 describes phosphoric esters (OH)3xe2x88x92nPOxe2x80x94(OR)n, and their salts wherein R is an aliphatic, cycloaliphatic and/or aromatic radical which contains at least one ether oxygen atom (xe2x80x94Oxe2x80x94) and at least one carboxylic acid grouping (xe2x80x94COOxe2x80x94) and/or urethane group (xe2x80x94NHCOOxe2x80x94), is devoid of Zerewitinov hydrogen, and has an average molecular weight of from 200 to 10000, it being possible for some of the hydrogen atoms of the aliphatic groups to have been replaced by halogen atoms, the ratio of the number of carboxylic ester groups and/or urethane groups in the molecule (or in each group R) is in the range from 1:20 to 20:1, and wherein n is 1 or 2. Also mentioned in particular is the use of these phosphoric esters as dispersants. Polyoxyalkylenecarbonyl monoether phosphates and their use as dispersants are also known from GB-A-19980429.
Also known is the use of such phosphoric esters to prepare emulsion polymers, in which context particular attention is drawn to the ready pigmentability of such emulsion polymers, especially those of low coagulum content (DE-A-19810658, JP-A-1 1246799 and WO 99/46337).
DE-A-19806964 describes particular phosphoric esters based on polystyrene-block (b)-polyalkylene oxide copolymers which are prepared from a monofunctional starter alcohol by sequential addition of styrene oxide and an alkylene oxide. Characteristics of these phosphoric esters include the use of at least 2 mol of styrene oxide for their preparation. Likewise described is the use of these phosphoric esters as dispersants for pigments and fillers. DE-A-19940797 describes the use of nonionic, block copolymeric, polyalkylene oxides containing styrene oxide as low-foam pigment wetting agents, the characteristics of the block copolymers including the use of less than 2 mol of styrene oxide for their preparation.
In the production of paints and inks, wetting agents and dispersants facilitate the incorporation of pigments and fillers, which are important formulating constituents that significantly determine the visual appearance and the physicochemical properties of coatings. Optimum use requires firstly that the solids are distributed uniformly in paints and inks and secondly that the state of distribution, once attained, is stabilized. In many cases, the stabilizing action is also undertaken by binder components. This is especially the case with acidic (styrene) acrylates, as used in particular for preparing printing inks. In these cases, pigment wetting agents are used whose action is to wet the pigment surface very rapidly and so to displace the air from the surface of the pigments by the liquid of the millbase. Especially when using solids having a nonpolar surface in aqueous paints, the wetting must be assisted by wetting agents. This permits favorable development of color strength and thus a near-ideal utilization of the input energy.
In the architectural paint industry in particular, moreover, use is made of aqueous pigment pastes, with or without cosolvents, which are used universally in aqueous emulsion paints on an all-acrylic, styrene acrylic or silicate basis and also in nonpolar decorative coatings based on long-oil alkyd, for tinting.
Particularly suitable for this purpose are the phosphoric esters of alkylphenol ethoxylates or fatty alcohol ethoxylates, which additionally contribute to steric and electrostatic stabilization of dispersed pigment states. The high-performance phosphoric esters of alkylphenol ethoxylates have come under criticism on ecotoxicological grounds, and their use is already regulated by legislators in a number of states. In many cases, the phosphoric esters of fatty alcohol ethoxylates fail to match the good properties of the alkylphenol ethoxylate derivatives. Since they lack adsorptive groups, the pigment wetting properties are less pronounced. Furthermore, the unadsorbed portion of this product group, in particular, has the unwanted effect of stabilizing the foam, which can be suppressed only with the aid of substances with a strong defoaming action which, in turn, bring about other adverse phenomena, such as unwanted surface defects. The use of a large number of dispersing additives also impacts negatively on the water resistance or light stability of coatings.
The known phosphoric esters have the disadvantage, moreover, that they are generally not suitable for universal use, since in many cases there is a lack of sufficient compatibility between dispersing additive and binder or dispersing additive and surrounding medium (aqueous or solventborne formulations). Furthermore, the chemical structure of the phosphoric esters has a large part to play: in aqueous formulations it is preferred to use only those phosphoric esters whose molecule does not contain any additional hydrolyzable functional groups, such as ester groups or urethane groups. Frequently, large additions of dispersing additives are necessary in order to suppress the occurrence of agglomerates; the degrees of filling that can be achieved are unsatisfactorily low, the stability of the dispersions and thus the constancy of their viscosity is often inadequate; flocculation and aggregation cannot always be avoided, so that there may be visible separation, leveling defects, and surface defects.
Applications of block copolymers containing styrene oxide in the paints and printing inks industry are still largely unknown. Those which are known include (DE-A-19806964) polystyrene oxide-block (b)-polyalkylene oxide copolymers which, starting from a monofunctional starter alcohol, are reacted to the corresponding phosphoric esters by sequential addition of at least 2 mol of styrene oxide and an alkylene oxide followed by phosphorylation. These block copolymers are likewise used as dispersants.
A disadvantage is the relatively poor biodegradability of these surfactants where the styrene oxide blocks are relatively long. Also of course, the diffusion mobility of dispersing additives of relatively high molecular mass is not particularly high, which is disadvantageous for rapid pigment wetting processes.
It was therefore an object of the present invention to meet the abovementioned requirements, the intention being that a high level of pigment affinity should go hand in hand with a low tendency towards foam stabilization and a high diffusion mobility without adversely affecting other essential coating properties.
This object is achieved in accordance with the invention, in a first embodiment, by block copolymeric phosphoric esters and their salts of the general formula (I)
[R1O(SO)a(EO)b(CH2CHCH3O)c(BO)d]xPOxe2x80x94(OH)3xe2x88x92xxe2x80x83xe2x80x83(I)
where
R1 a straight-chain or branched or cycloaliphatic radical, preferably having 1 to 22 carbon atoms,
SO=styrene oxide,
EO=ethylene oxide,
BO=butylene oxide and
a=1 to  less than 2, preferably to 1.9,
b=3 to 100,
c=0 to 1,
d=0to 3,
x=1 or 2,
where bxe2x89xa7a+c+d, in particular by their use as pigment wetting agents for pigment pastes, aqueous, solventborne, low-solvent and solvent-free paints and printing inks. The phosphoric esters of the general formula I are used in particular in an amount of from about 2 to about 200% by weight, based on the weight of the respective pigment.
An important factor with respect to the properties of the compounds are the numerical values of the indices a, b, c and d. a indicates the number of styrene oxide groups, which especially in the case of hydrophobic pigment surfaces ensure high adsorption. a here has a value of 1 to  less than 2, in particular to 1.9. b defines the number of ethylene oxide groups, it being possible for b to adopt values from 3 to 100, preferably from 10 to 30. c defines the number of propylene oxide groups and has a value of from 0 to 10, preferably from 1 to 3. d defines the number of butylene oxide groups and has a value from 0 to 3, preferably 0 or 1. The skilled worker is well aware that the compounds are in the form of a mixture having a distribution governed essentially by statistical laws. The alkoxylates to be used in accordance with the invention are mixed alkoxylates. By means of the various alkylene oxide monomers and their fraction in the total polymer it is possible specifically to control the hydrophobic/hydrophilic balance such that any steric requirements of the pigment surface and, in particular, the compatibility in the respective coating system may be tailored accordingly. The alkylene oxide groups may be arranged randomly or in blocks. Particular preference is given to block arrangements containing terminal, preferably hydrophobic groups such as propylene oxide or, in particular, butylene oxide. The molar ratio of the ethylene oxide groups to the other hydrophobic alkylene oxide groups is: bxe2x89xa7a+c+d. It has been found that the structures of the polymers are of critical importance to the advantages achieved in accordance with the invention. Preferably, the respective alkylene oxide groups are present in the stated sequence of the general formula I. However, any other sequences desired are also included in the description.
Of similar significance are the structures of the straight-chain or branched or cycloaliphatic radicals R1, by which the space occupancy of these surfactants at interfaces can be controlled. For many applications, branched aliphatic radicals R1 are advantageous, for the purpose of suppressing foam. Particular preference is therefore given to branched C9 alcohols as starting agents for the alkoxylation. Particular preference is given to 3,5,5-trimethylhexan-1-yl and 2,6-dimethylheptan-4-yl radicals; the skilled worker is well aware that the parent alcohols are in the form, in particular, of isomeric mixtures, the particular isomer mixture being heavily dependent on the respective process conditions.
The preparation of the hydroxy-functional, block copolymeric polyalkylene oxides containing styrene oxide, which are starting materials for the phosphoric esters to be used in accordance with the invention, has already been described in principle in DE-A-19940797.
Conversion into the phosphoric esters to be used in accordance with the invention takes place by reacting the terminal hydroxyl groups with a phosphorus compound which forms phosphoric esters, in a manner corresponding to the prior art. Suitable phosphorus compounds are, for example, phosphorus pentoxide, phosphoryl chloride or polyphosphoric acids of the general formula Hn+2PnO3n+1. To prepare the phosphoric esters, particular preference is given to using a commercially available polyphosphoric acid having a P4O10 content of approximately 85% by weight. The reaction generally takes place without solvents at temperatures from about 60 to 120xc2x0 C., in particular at temperatures from 80 to 100xc2x0 C. To remove any traces of moisture present it is possible first to remove residues of water from the system using an inert solvent, such as toluene or xylene, for example, before the reaction with the polyphosphoric acid. In principle, however, the reaction may also take place in the presence of solvents or solvent mixtures.
The terminal hydroxyl groups, intended for esterification, in the amphiphilic block copolymers is esterified preferably to a level of from 50 to 100%, with particular preference quantitatively, in the esterification reaction. Depending on the amount that is used of the phosphorus compound which forms phosphoric esters, based on the hydroxy equivalent of the block copolymers, the products are alternatively preferentially monoesters, diesters, or mixtures of monoesters and diesters.
Depending on the pH of the medium in which they are employed, the phosphoric esters for use in accordance with the invention may also be in partially or fully neutralized form. In this case, as the counterions, mention may be made in particular of alkali metal and alkaline earth metal ions and also substituted or unsubstituted ammonium ions.
Examples of phosphoric esters for use in accordance with the invention are:
a) ((3,5,5-trimethyl-1-hexanol)(SO)1(EO)5)1PO(OH)2 
b) ((3,5,5-trimethyl-1-hexanol)(SO)1(EO)9)1PO(OH)2 
c) ((1-nonanol)(SO)1(EO)9)1PO(OH)2 
d) ((2,6-dimethyl-4-heptanol)(SO)1(EO)9(BO)3)1PO(OH)2 
e) ((3,5,5-trimethyl-1-hexanol)(SO)1.9(EO)12)1PO(OH)2 
f) ((1-nonanol)(SO)1(EO)9(CH2CHCH3)3)1PO(OH)2 
Aqueous pigment pastes are prepared using from about 2.0 to about 200% by weight of the phosphoric esters for use in accordance with the invention, preferably from about 5.0 to about 100% by weight (based on the weight of the pigments). When used in accordance with the invention, alone or in combination, the phosphoric esters may be either mixed beforehand with the pigments to be dispersed or dissolved directly in the aqueous or solvent-containing dispersing medium, prior to or simultaneously with the addition of the pigments and any solids. Occasionally it is also preferred to apply the phosphoric estersxe2x80x94by spraying, for examplexe2x80x94to the solids that are to be dispersed, prior to the dispersing process.
The skilled worker is well aware that the phosphoric esters can of course also be combined with other, conventional pigment-wetting additives and resins.
The invention further relates to the use of the pigment preparations according to the invention to pigment natural or synthetic materials. They are particularly suitable for tinting nonpolar decorative paints based on long-oil alkyds, but also for preparing emulsion paints, aqueous flexographic and gravure inks, wallpaper inks, aqueous wood preservative systems and aqueous wood stains, plasters, and also to pigment colored pencil leads, fibertip pens, inkjet inks, drawing inks, and ballpoint pen pastes.
Examples of pigments that may be used in this context are organic and inorganic pigments and also carbon blacks.
As inorganic pigments, mention may be made by way of example of titanium dioxides and iron oxides. Examples of organic pigments for consideration are azo pigments, metal complex pigments, anthraquinonoid pigments, phthalocyanine pigments, polycyclic pigments, especially those of the thioindigo, quinacridone, dioxazine, pyrrolopyrrole, naphthalenetetracarboxylic acid, perylene, isoamidolin(on)e, flavanthrone, pyranthrone or isoviolanthrone series. With particular preference, the dispersing additives for use in accordance with the invention are suitable for preparing aqueous carbon black pastes.
Examples of fillers which may be dispersed, for example, in aqueous paints are those based on kaolin, talc, other silicates, chalk, glass fibers, glass beads or metal powders.
Suitable coating systems into which the pigment pastes prepared in accordance with the invention may be incorporated include any desired one-component (1K) or two-component (2K) coatings, and also nonpolar low-solvent or solvent-free coating systems. Examples that may be mentioned include aqueous 1K coating materials, such as those based on alkyd, acrylic, epoxy, polyvinyl acetate, polyester or polyurethane resins, or aqueous 2K coating materials, examples being those based on hydroxyl-containing polyacrylate resins or polyester resins with melamine resins or optionally blocked polyisocyanate resins as crosslinkers. Similarly, mention may also be made of polyepoxide systems. As low-solvent coating materials, particular mentioned may be made of those based on long-oil alkyds.
Moreover, these highly effective anionic surfactants are highly effective emulsifiers and as such are ideally suited, for example, to the preparation of low-coagulum emulsion polymers characterized by high pigment acceptance. In this case too, the phosphoric esters for use in accordance with the invention may be used alone or in combination.
Analogously, the polyalkylene oxides which serve as precursors for the synthesis of the phosphate esters may also be used, in accordance with prior art processes using known sulfating and sulfonating reagents, to prepare new kinds of sulfate esters and sulfonate esters. Compounds of this kind containing styrene oxide as alkylene oxide monomer have not been disclosed to date. It is assumed that these novel compounds may be used in the same way as the phosphate esters described here for dispersing pigments or stabilizing emulsions.